Laundry washing machines conventionally receive a controlled amount of water at the outset of a wash cycle, to saturate the articles of clothing or other laundry placed in a wash basket thereof, and to provide an additional amount of “free water,” (i.e., water in the wash tub not absorbed by the clothes) within which the load of laundry may be agitated to induce cleansing during the wash cycle. Typically, the wash basket is a perforated container, rotatably mounted within an outer stationary tub serving to hold the wash liquid. In a conventional arrangement, the water level in the tub is determined by a user-selected load size setting. For example, the user selects from a number of load size settings (e.g., ‘Small’, ‘Medium’, or ‘Large’), and based on that selection, water is added to the wash tub until a predetermined pressure reading is reached, corresponding to the user-selected load size, whereupon the washer fill is terminated and the next wash cycle (e.g., agitation) commences.
Certain shortcomings are inherent in this conventional technique. Namely, the user-selected load size might not correspond to the actual size of the load of clothes in the wash basket. For instance, a user selecting a large load size for washing just a few clothing items will unnecessarily waste both water, and energy used to heat the water, during the wash cycle. Similarly, a user selecting too small a load size for the clothing load may not supply enough free water to the wash tub for optimal cleansing of the clothes during the wash cycle.
Previous attempts have been made to improve upon the above-described conventional technique for filling a wash tub. U.S. Pat. No. 5,408,716 to Dausch et al. describes a technique which involves measuring pressure surges and cavitations at a sensor positioned beneath the tub, and filling the tub until cavitation substantially decreases. This decrease in cavitation is interpreted as an indication that the tub contains an adequate amount of water for washing the load.
Another technique for filling a wash tub is described in U.S. Pat. No. 4,697,293 to Knoop. This technique involves monitoring the water level during an initial tub fill with a pressure sensor to reach a predetermined minimum water level. A low speed agitation is then engaged using a vertically oriented agitator inside the wash basket, while pressure readings continue to be recorded. The pressure oscillation ranges are used to estimate the load size, then the tub is filled with additional water as needed to reach the predetermined optimum water level based on the estimated load size and user-selected fabric type.
U.S. Pat. No. 4,835,991 to Knoop et al. discloses a technique similar to the earlier Knoop patent for controlling the water fill level. In this technique, a maximum rollover rate of the clothes is determined based on the oscillation range of pressure readings during agitation, and the water fill level is controlled accordingly.
Despite the previous attempts to improve upon the conventional wash tub filling process, there remains a need for a wash tub filling process that can efficiently and accurately regulate the amount of water dispensed into the wash tub based on the load size.